Subject: Re: [syzbot] linux-next test error: WARNING in set_peer

From: Kees Cook <[email-masked]>
Date: Tue, 13 Sep 2022 17:55:39 -0700

On Tue, Sep 13, 2022 at 12:51:42PM -0700, syzbot wrote:
> memcpy: detected field-spanning write (size 28) of single field "&endpoint.addr" at drivers/net/wireguard/netlink.c:446 (size 16)

This is one way to fix it:

diff --git a/drivers/net/wireguard/netlink.c b/drivers/net/wireguard/netlink.c
index 0c0644e762e5..dbbeba216530 100644
--- a/drivers/net/wireguard/netlink.c
+++ b/drivers/net/wireguard/netlink.c
@@ -434,16 +434,16 @@ static int set_peer(struct wg_device *wg, struct nlattr **attrs)
 	}
 
 	if (attrs[WGPEER_A_ENDPOINT]) {
-		struct sockaddr *addr = nla_data(attrs[WGPEER_A_ENDPOINT]);
+		struct endpoint *raw = nla_data(attrs[WGPEER_A_ENDPOINT]);
 		size_t len = nla_len(attrs[WGPEER_A_ENDPOINT]);
 
 		if ((len == sizeof(struct sockaddr_in) &&
-		     addr->sa_family == AF_INET) ||
+		     raw->addr.sa_family == AF_INET) ||
 		    (len == sizeof(struct sockaddr_in6) &&
-		     addr->sa_family == AF_INET6)) {
+		     raw->addr.sa_family == AF_INET6)) {
 			struct endpoint endpoint = { { { 0 } } };
 
-			memcpy(&endpoint.addr, addr, len);
+			memcpy(&endpoint.addrs, &raw->addrs, len);
 			wg_socket_set_peer_endpoint(peer, &endpoint);
 		}
 	}
diff --git a/drivers/net/wireguard/peer.h b/drivers/net/wireguard/peer.h
index 76e4d3128ad4..4fbe7940828b 100644
--- a/drivers/net/wireguard/peer.h
+++ b/drivers/net/wireguard/peer.h
@@ -19,11 +19,13 @@
 struct wg_device;
 
 struct endpoint {
-	union {
-		struct sockaddr addr;
-		struct sockaddr_in addr4;
-		struct sockaddr_in6 addr6;
-	};
+	struct_group(addrs,
+		union {
+			struct sockaddr addr;
+			struct sockaddr_in addr4;
+			struct sockaddr_in6 addr6;
+		};
+	);
 	union {
 		struct {
 			struct in_addr src4;

diffoscope shows the bounds check gets updated to the full union size:
│ -     cmp    $0x11,%edx
│ +     cmp    $0x1d,%edx

and the field name changes in the warning:
$ strings clang/drivers/net/wireguard/netlink.o.after | grep ^field
field "&endpoint.addrs" at drivers/net/wireguard/netlink.c:446

-- 
Kees Cook